The following relates generally to wireless communication and more specifically to codebook restriction and sub-sampling for channel state information (CSI) reporting.
Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include fourth generation (4G) systems such as a Long Term Evolution (LTE) systems or LTE-Advanced (LTE-A) systems, and fifth generation (5G) systems which may be referred to as New Radio (NR) systems. These systems may employ technologies such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), or discrete Fourier transform-spread-OFDM (DFT-S-OFDM). A wireless multiple-access communications system may include a number of base stations or network access nodes, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE).
In some wireless communications systems, a UE may be configured to report CSI to a base station. The base station may use the CSI to identify appropriate configurations for transmitting downlink signals to the UE. In one example, a UE may transmit a precoding matrix indicator (PMI) to the base station in a CSI report. The PMI may identify a preferred precoding matrix for the base station to use to precode downlink transmissions to the UE, and the UE may identify the preferred precoding matrix from a range of different precoding matrices (e.g., a codebook of precoding matrices). In some cases, the number of possible precoding matrices that the UE may evaluate to identify the preferred precoding matrix may be large. As a result, the latency associated with the CSI reporting process may be high, which may be detrimental to a wireless communications system.